Printed flexible wiring apparatus in a cryostat

ABSTRACT

A novel and useful system wiring apparatus and related techniques that address the need to feed power and electronic signals to and from a sample board between the cold, low pressure region in a vacuum chamber and outside room temperature and atmospheric pressure. The wiring apparatus balances electrical resistance with the thermal conductivity of the power and signal conductors. Printed flexible cables are used having an annular sealing region which together with O-rings provide vacuum sealing while allowing electrical signals to pass between integrated circuit(s) inside the vacuum chamber and equipment outside the chamber. A thermal anchor is placed along the printed flexible cable to maintain a desired temperature along the cable. The printed flexible circuits are multilayer with two outer layers serving as an RF shield while two inner layers comprise the signal lines which typically require shielding, electrical isolation from each other and from external electromagnetic fields.

FIELD OF THE DISCLOSURE

The subject matter disclosed herein relates to the field of quantumcomputing and more particularly relates to a cryostat system includingprinted flexible cables, vacuum sealing, and suspended sample board.

BACKGROUND OF THE INVENTION

Quantum computing is a new paradigm that exploits fundamental principlesof quantum mechanics, such as superposition and entanglement, to tackleproblems in mathematics, chemistry and material science that are wellbeyond the reach of supercomputers. Its power is derived from a quantumbit (qubit), which can simultaneously exist as a superposition of both 0and 1 states and can become entangled with other qubits. This leads todoubling the computational power with each additional qubit, which canbe repeated many times. It has been already shown that quantum computerscan speed up some of the algorithms and, potentially, model any physicalprocess.

Operating electronics including quantum circuits under cryogenicconditions (i.e. temperatures below −180° C./93K) is useful for theoperation of certain types of silicon devices, such as thermal detectorsand quantum computer circuitry. Maintaining cryogenic conditions in anexperimental or operational region requires a heat pump to remove theheat from that region, and a cryostat to minimize the heat transfer fromthe surroundings back into the region.

There is also a need to provide a path for electrical signals includingdata, control, and power lines to enter and exit the cold, low pressureregion inside a vacuum chamber from the outside which is typically atroom temperature and at atmospheric pressure while providing asufficient seal to maintain the vacuum within the chamber.

SUMMARY OF THE INVENTION

The following summary is illustrative only and is not intended to belimiting in any way. That is, the following summary is provided tointroduce concepts, highlights, benefits and advantages of the novel andnon-obvious techniques described herein. Select implementations arefurther described below in the detailed description. Thus, the followingsummary is not intended to identify essential features of the claimedsubject matter, nor is it intended for use in determining the scope ofthe claimed subject matter.

The present invention is a wiring apparatus and related techniques thataddress the need to feed power and electronic signals into and out ofthe cold, low pressure region in a vacuum chamber to the outside whichis typically at room temperature and atmospheric pressure. The wiringapparatus also functions to balance electrical resistance with thethermal conductivity of the power and signal conductors. Copper is mostoften used to transmit electronic signals, but as stated supra, it isalso used as a good thermal conductor. Note that thermal conductivityand electrical conductivity are related by the Wiedemann-Franz law whichstates that the ratio of the electronic contribution of the thermalconductivity (κ) to the electrical conductivity (σ) of a metal isproportional to the temperature (T).

In the development of cryo-electronic systems, it is preferable toproduce wiring solutions that can be assembled consistently, and thatcan be modified quickly and cost effectively, in order to more quicklydetermine the correct balance between thermal and electronicperformance. When mass producing such cryo-electronic systems, it isalso important to maximize component functionality and reliability whileminimizing complexity, part count and ultimately cost.

In one embodiment, both the TV flex printed circuit as well as the cryoflex printed circuit are multilayer and in one example embodimentcomprise four layers. The two outer layers serve as electromagneticshields while the two inner layers comprise the signal lines whichtypically require electromagnetic shielding, electrical isolation fromeach other and from external electromagnetic fields. In one embodiment,the electromagnetic shield is not solid and comprises a mesh pattern(e.g., diamond, hexagons, octagons, or other polygon shape) making itmore flexible. Preferably, the RF cutoff frequency of the printed shieldis high enough to act as a solid shield without creating too muchconductance. The mesh preferably minimizes conductivity while stillproviding sufficient RF shielding. Thus, the cable enables effectiveshielding by optimizing the scale and size of the mesh, while minimizingthe total cross sectional area of copper running up and down the flexcables, and therefore its thermal conductivity.

There is thus provided in accordance with the invention, a flexiblewiring apparatus for use in a cryostat, comprising a first flexibleprinted circuit adapted to be sealed in a vacuum chamber of the cryostatand having a plurality of electrically conductive traces for passingelectrical signals between an air side and a vacuum side of thecryostat, a second flexible printed circuit coupled to a sample boardheld at a first cryogenic temperature, an electrical connector operativeto electrically couple the first flexible circuit to the second flexiblecircuit while providing thermal isolation between the first flexiblecircuit and the second flexible circuit, and a thermal anchor operativeto clamp the second flexible circuit to a second cryogenic temperaturethereby providing a thermal breakpoint between the first cryogenictemperature within the vacuum chamber and ambient temperature outsidethe vacuum chamber.

There is also provided in accordance with the invention, a flexiblewiring apparatus for use in a cryostat, comprising a flexible printedcircuit, including a flat laminated flexible material having an annularshaped sealing region able to be vacuum sealed between a cover plate anda perimeter of a hole in a vacuum chamber of the cryostat, a pluralityof electrically conductive traces that cross the annular shaped regionthereby passing electrical signals between an air side and a vacuum sideof the cryostat, a first PCB assembly terminating the plurality ofelectrically conductive traces on the air side of the cryostat forconnection to an external host computer, a second PCB assemblyterminating the plurality of electrically conductive traces on thevacuum side of the cryostat for connection to a sample circuit boardcontaining an integrated circuit cooled to a first cryogenictemperature, and a thermal anchor operative to clamp the flexibleprinted circuit to a second cryogenic temperature thereby providing athermal breakpoint between the first cryogenic temperature within thevacuum chamber and atmospheric temperature outside the vacuum chamber.

There is further provided in accordance with the invention, a flexiblewiring apparatus for use in a cryostat, comprising a first flexibleprinted circuit, including a flat laminated flexible material having anannular shaped sealing region able to be vacuum sealed between a coverplate and a perimeter of a hole in a vacuum chamber of the cryostat, aplurality of electrically conductive traces that cross the annularshaped region thereby passing electrical signals between an air side anda vacuum side of the cryostat, a second flexible printed circuit coupledto a sample board held at a first cryogenic temperature, an electricalconnector operative to electrically couple the first flexible circuit tothe second flexible circuit while providing thermal isolation betweenthe first flexible circuit and the second flexible circuit, and athermal anchor operative to clamp the second flexible circuit to asecond cryogenic temperature thereby providing a thermal breakpointbetween the first cryogenic temperature within the vacuum chamber andambient temperature outside the vacuum chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in further detail in the followingexemplary embodiments and with reference to the figures, where identicalor similar elements may be partly indicated by the same or similarreference numerals, and the features of various exemplary embodimentsbeing combinable. The invention is herein described, by way of exampleonly, with reference to the accompanying drawings, wherein:

FIG. 1A is a perspective view diagram illustrating a first examplecryostat system constructed in accordance with the present invention;

FIG. 1B is a perspective view diagram illustrating a second examplecryostat system constructed in accordance with the present invention;

FIG. 2A is a diagram illustrating a top layer of a first exampletrans-vacuum flexible printed circuit having rigid printed circuit boardtabs;

FIG. 2B is a diagram illustrating a middle layer of a first exampletrans-vacuum flexible printed circuit having rigid printed circuit boardtabs;

FIG. 2C is a diagram illustrating a top view of a second exampletrans-vacuum flexible printed circuit having rigid printed circuit boardtabs;

FIG. 2D is a diagram illustrating a cross sectional view of a firstexample trans-vacuum flexible printed circuit;

FIG. 2E is a diagram illustrating a cross sectional top view of a firstexample trans-vacuum flexible printed circuit rigid printed circuitboard tabs;

FIG. 2F is a diagram illustrating a top view of a cryostat flexibleprinted circuit having rigid printed circuit board tabs;

FIG. 3A is a diagram illustrating a side view of the example cryostatsystem using two printed flexible cables;

FIG. 3B is a diagram illustrating a side view of the example cryostatsystem using a single printed flexible cable;

FIG. 4 is a diagram illustrating a cross sectional view of the examplecryostat system including heat shield and cooling tower;

FIG. 5 is a diagram illustrating a side view of the example cryostatsystem showing the cryostat cable in more detail;

FIG. 6 is a diagram illustrating the connector interface between the twoflex cables in more detail;

FIG. 7 is a diagram illustrating the suspended sample board mechanism inmore detail;

FIG. 8 is a diagram illustrating an outside view of an exampletrans-vacuum flexible printed circuit installed in a vacuum chamber witha rigid printed circuit board tab extending outward;

FIG. 9 is a diagram illustrating a forward cutaway view of an exampletrans-vacuum flexible printed circuit installed in a vacuum chamber withan O-ring seated against an annular sealing region;

FIG. 10 is a diagram illustrating a rear cutaway view of an exampletrans-vacuum flexible printed circuit installed in a vacuum chamber withan O-ring seated against an annular sealing region;

FIG. 11A is a diagram illustrating a sectional view of a first exampletrans-vacuum flexible printed circuit installed in a vacuum chamber withan annular sealing region sandwiched between two O-rings;

FIG. 11B is a diagram illustrating a sectional view of a second exampletrans-vacuum flexible printed circuit installed in a vacuum chamber withan annular sealing region sandwiched between two O-rings; and

FIG. 12 is a diagram illustrating example RF signal cables extendingfrom the trans-vacuum flexible printed circuit to the suspended sampleboard.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention. Itwill be understood by those skilled in the art, however, that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Among those benefits and improvements that have been disclosed, otherobjects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingfigures. Detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the invention that may be embodied in variousforms. In addition, each of the examples given in connection with thevarious embodiments of the invention which are intended to beillustrative, and not restrictive.

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings.

The figures constitute a part of this specification and includeillustrative embodiments of the present invention and illustrate variousobjects and features thereof. Further, the figures are not necessarilyto scale, some features may be exaggerated to show details of particularcomponents. In addition, any measurements, specifications and the likeshown in the figures are intended to be illustrative, and notrestrictive. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention. Further, where considered appropriate,reference numerals may be repeated among the figures to indicatecorresponding or analogous elements.

Because the illustrated embodiments of the present invention may for themost part, be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary, for the understanding andappreciation of the underlying concepts of the present invention and inorder not to obfuscate or distract from the teachings of the presentinvention.

Any reference in the specification to a method should be applied mutatismutandis to a system capable of executing the method. Any reference inthe specification to a system should be applied mutatis mutandis to amethod that may be executed by the system.

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The phrases “in one embodiment,” “in an exampleembodiment,” and “in some embodiments” as used herein do not necessarilyrefer to the same embodiment(s), though it may. Furthermore, the phrases“in another embodiment,” “in an alternative embodiment,” and “in someother embodiments” as used herein do not necessarily refer to adifferent embodiment, although it may. Thus, as described below, variousembodiments of the invention may be readily combined, without departingfrom the scope or spirit of the invention.

In addition, as used herein, the term “or” is an inclusive “or”operator, and is equivalent to the term “and/or,” unless the contextclearly dictates otherwise. The term “based on” is not exclusive andallows for being based on additional factors not described, unless thecontext clearly dictates otherwise. In addition, throughout thespecification, the meaning of “a,” “an,” and “the” include pluralreferences. The meaning of “in” includes “in” and “on.”

A perspective view diagram illustrating a first example cryostat systemconstructed in accordance with the present invention is shown in FIG.1A. The cryostat, generally referenced 60, comprises a cold head 62 andmounting plate 64 that sit outside the vacuum chamber and extendsthrough an opening at the top downward towards the sample board near thebottom. The cryocooler includes concentric tubes or shafts that providetwo stages of cooling. The top portion 80 of the cryocooler shaft coolsthe first stage 78 to approximately 30 kelvin (i.e. 30K). The bottomportion 96 of the cryocooler shaft cools the second stage 90 and coldmounting plate 94 to approximately 3 degrees K.

In one embodiment, the cryostat employs a vacuum (or partial vacuum) toremove the gases that would conduct and convect external heat back intothe region, polished surfaces, gold plating to minimize heat radiationinto the region, certain materials such as stainless steel (a poor heatconductor) to minimize conduction where needed, and copper (an excellentheat conductor) to maximize heat conduction where needed.

In another embodiment, the TV flex circuit is mounted on the top of thevacuum chamber. The top of the chamber is where the cryogenic coolerapparatus passes through a hole in the vacuum chamber as well as acorresponding hole in the TV flex circuit. Vacuum sealing utilizesO-rings to seal against the annular sealing region portion of the flexcircuit. A spiral tab extending into the vacuum chamber is adapted tohave a path around the cryogenic cooler head assembly.

A trans-vacuum (TV) flexible circuit or wiring apparatus 66 functions toprovide electrical connections between outside the vacuum chamber viaconnector 68 and the sample board via PCB assembly 92. The TV flexcircuit has an annular ring portion 70 that forms part of the vacuumseal. Electrical connections cross the annular ring and form a spiralpath 72 around the cooling shaft 80 to a PCB assembly 76. A plurality ofholes 74 allow for fasteners to secure a cover plate. A second flexiblecircuit cable 86 (also referred to as a cryo-flex cable) is coupled tothe TV flex cable via PCB assembly 84 and connector 82. In oneembodiment, the PCB assembly 76 is mounted to the first stage cold plate78 which is held at approximately degrees K. To address convention andradiative heat loss, the first and second stage cold plates 78, 90 aresolid copper and plated with gold to make them very reflective.

The cryo-flex cable passes through a thermal anchor 88 that clamps thetemperature at that point in the cable to the first stage temperature ofapproximately 30 degrees K. The cryo-flex cable forms a loop between thethermal anchor 88 and the connector 82. The connector is adapted toprovide good electrical conductivity but poor thermal conductivity toprovide a degree of thermal isolation between the two flex cables. Thecryo-flex cable 86 continues downward along the cooling shaft 96 to thecold mounting/fastening plate 94 and second stage which is maintained at3K. In addition, since the PCB assembly 76 is clamped to the firstcooling stage which has far more cooling capacity (e.g., 50 W) than thesecond cooling stage (e.g., 200 mW), it is preferable to place at thefirst stage location any power hungry circuitry such as RF attenuators,amplifiers, and/or power supply regulators which are used to reducenoise in the RF signals. Other circuitry such as transceiver circuits orintermediate amplifier circuits for high speed communication can also beplaced at this location.

It is noted that using two flex cables with a thermal break andelectrical connection between them (i.e. two stage design of TV-flex andcryo-flex cables) versus using a single cable is far more energyefficient. Use of two cables in going from 300K to 30K and then 30K to3K lowers the energy loss than use of a single cable with the sametemperature span of 300K to 3K. This is because any kind of thermalcontact that must be cooled to 3K consumes much more energy comparedwith being cooled first to 30K and then to 3K. Note that the thermalconductivity of copper increases as it is cooled and has a peak atapproximately 20K. Although copper is a good electrical conductor it isalso a good thermal conductor which is not desirable in this case insidethe cryostat vacuum chamber. This is because the 3K at the second stagesample board can creep along the copper traces of the printed flexiblecable. As each further region of copper is cooled, its thermalconductivity increases and losses would also increase along the path ofthe cable. Thus, the thermal anchor stops this process from continuingalong the cable.

In one embodiment, the flex circuits comprise four layers with the twoouter layers functioning as RF shielding. The electromagnetic shieldinglayers may be solid metal but to improve flexibility at low temperaturesthey preferably have a non-solid pattern. For example a honeycomb,diamond, octagonal, hexagonal, or other polygon shaped pattern ofrelatively thin traces can be used, which yield a minimum amount ofmetal (e.g., copper) to provide RF shieling while retaining flexibilityat low temperatures and also minimizing thermal conductivity along thecable. The multiple layers of the cable provide electrical isolationbetween the individual signal traces whether single ended or balanced,differential, as well as isolation from external electromagnetic fields.Further, the RF and microwave lines of the flex cables can be impedancecontrolled and well isolated from each other in left, right, up, anddown directions in relation to their position in the cable, whichimproves performance. Thus, the cable can enable effective shielding byoptimizing the scale and size of the mesh, while minimizing the totalcross sectional area of copper running up and down the flex cables, andtherefore its thermal conductivity.

Note that the shielding is solid and planar and not a mesh in the outertwo layers of the cable in the region of the annular vacuum seal of theTV flex circuit. This is because O-rings that provide the sealing preferto seal against a solid planar surface and not the thin mesh pattern ofthe shield.

Note further that the width and thickness of the copper traces used inthe flex cables may be fabricated having any desired size in order tomanage their electrical and thermal conductivity in accordance with theparticular implementation of the invention.

A perspective view diagram illustrating a second example cryostat systemconstructed in accordance with the present invention is shown in FIG.1B. This embodiment is similar to the TV flex circuit of FIG. 1A withthe difference being that the spiral portion 72 of the circuit isreplaced with a straight portion 73 that leads to connector 82.

A diagram illustrating a top (and bottom) layer of a first exampletrans-vacuum flexible printed circuit having rigid printed circuit boardtabs is shown in FIG. 2A. A diagram illustrating inner electrical signallayers of a first example trans-vacuum flexible printed circuit havingrigid printed circuit board tabs is shown in FIG. 2B.

The trans-vacuum (TV) flexible circuit or wiring apparatus, generallyreferenced 10, comprises an annular sealing region 12 adapted to receiveone or more O-rings to create a vacuum seal around the perimeter of anopening in a vacuum chamber. The TV flex circuit also comprises aplurality of electrical traces 15 that run between two rigid printedcircuit board (PCB) edge connectors 18, 20. The electrical traces 15extend through a flex tab 16, cross the annular sealing region 12through a gap 13 in the RF shielding mesh 17 and continue through tab 14to rigid PCB connector 20.

The TV flex circuit uses well-known printed circuit board flex circuittechnology to integrate a vacuum seal with the electrical conductorsthat need to pass through from the air side to the vacuum side of acryostat. In one embodiment, the TV flex circuit enables the feedthroughof up to 84 separate signals with less than 50 mW thermal power penalty.

Note that in this example embodiment, the electrical traces crossaxially or perpendicular to the annular sealing region. In alternativeembodiments, the electrical traces cross tangentially at any desiredangle depending on the particular application. In addition, flex tab 14is shown having a shape of a spiral in order to maximize the length ofthe flex tab during manufacture. Alternatively, the flex tab 14 can haveany desired shape and is not limited to a spiral shape.

As described supra, the TV flex cable comprises an RF shield mesh 17 onits two outer layers. In the area of the annular sealing regiondelineated by the dashed concentric circles 11 and extending to theedges of the flex circuit, however, a solid or semi-solid pattern 19replaces the mesh 17 in order to enable better vacuum sealing againstthe O-rings. On the signal layers, a gap 13 in the solid or semi-solidpattern 19 is placed on either side of the signal traces 15.

A diagram illustrating a top view of a second example trans-vacuumflexible printed circuit having rigid printed circuit board tabs isshown in FIG. 2C. In this embodiment, two TV flex cables are mated intoa single assembly. This is useful for the case where the cryostatincorporates two cold heads rather than one. The two cold headspenetrate the vacuum chamber and the TV flex printed circuits provide apath for electrical signals and power to enter and exit the vacuumchamber while providing sealing around the two openings. The operationof each of the two TV flex cables is the same as in the single TV flexcable case described supra. Note that in an alternative embodiment thecryostat may comprise more than two cold heads and correspondingadditional TX flex printed circuits.

A diagram illustrating a cross sectional view of a first exampletrans-vacuum flexible printed circuit is shown in FIG. 2D. In oneembodiment, the TV flex cable 150 comprises four electrical layers 156,160, 164, 168 surrounded by several outer layers. The outer layers 152,172 comprise cover layers of polyimide. The layers below these, namely154, 170, comprise adhesive acrylic and/or polyimide. The top and bottomelectrical layers 156, 168 comprise copper mesh 17 that functions as RFelectromagnetic shielding. The internal electrical layers 160, 164comprise copper signal traces. The four electrical layers are separatedby dielectric layers 158, 162, 166 that may comprise polyimide or anadhesive thermoset material. In addition, the inner dielectric layer 162separating the signal layers 160, 164 may be thicker, e.g., 4.6 milversus 1.0 mil for layers 158, 166. In addition, the copper signaltraces in all four electrical layers are made as thin as practical tominimize thermal conductivity while also providing sufficient electricalconductivity.

A diagram illustrating a cross sectional top view of a first exampletrans-vacuum (TV) flexible printed circuit rigid printed circuit boardtabs is shown in FIG. 2E. In one embodiment, the rigid PCB 180 compriseseight layers including four electrical copper layers 196, 199, 202, 206and four electrical copper PCB layers 188, 192, 210, 214, four polyimidedielectric PCB layers 190, 194, 208, 212. The electrical layers 196,199, 202, 206 are separated by dielectric layers 198, 200, 204 that maycomprise polyimide or an adhesive thermoset material. The PCB layers aresurrounded by solder paste layers 186, 216, adhesive acrylic layers 184,218, and polyimide cover layers 182, 220. Electrical connections betweenthe signal traces in the flexible cable and the copper conductor PCBlayers are made using a plurality of vias. This requires accuratealignment of the flex circuit and PCB layers. Thus, the terminal ends ofthe TV flex cable are sandwiched during manufacturing between multiplePCB layers. These rigid PCB assemblies at either end of the cablecomprise a plurality of edge connectors and in addition may comprisecircuitry and other components depending on the implementation.

A diagram illustrating a top view of a cryostat flexible printed circuithaving rigid printed circuit board tabs is shown in FIG. 2F. Thecryostat flexible printed cable 86 is terminated on either end by rigidPCB tabs 84, 92. In one embodiment, the cryostat flexible printed cableis constructed similarly to the TV flex printed cable with the differentbetween that the cryostat flexible printed cable comprises twoelectrical layers instead of four. In this case, the two electricallayers comprise signal layers as the RF electromagnetic shielding layersare not necessary as the cable resides completely within theelectrically insulated vacuum chamber.

Similar to the TV flex printed cable described supra, several PCB layerssurround the ends of the cryostat flexible printed cable to form therigid PCB assemblies 84, 92. Electrical connections between the signaltraces in the cryostat flexible cable and the copper conductor PCBlayers are made using a plurality of vias. This typically requiresaccurate alignment of the flex circuit and PCB layers duringmanufacturing.

A diagram illustrating a side view of the example cryostat system thatuses two printed flexible circuits is shown in FIG. 3A. The cryostat,generally referenced 60, comprises a cold head 62, mounting plate 64,TV-flex circuit 66, connector 68 that connects to outside the vacuumchamber, cryocooler first stage shaft 80, first stage plate 78, saddle88 and anvil 89, TV-flex PCB connector 76, thermal isolating connector82, cryo-flex PCB connection 84, cryocooler second stage shaft 96,second stage plate 90, and PCB assembly 92. Note that to optimizethermal conductivity, the copper used for the first and second stageplates may comprise annealed copper as annealed copper's thermalconductivity is much higher at low temperatures (e.g., 10K).

This figure highlights the spiral path 72 of the TV-flex cable 66 aroundthe first stage cooling shaft 80. The annular sealing region is clampedbetween the vacuum cover and the housing. Also highlighted is thethermal anchor consisting of matched thermally conductive components 88,89 that clamp the cryo-flex cable 86 to the first stage temperature of30K. For example, the matched thermally conductive components maycomprise matched concave and convex components such as a saddle andmatching complimentary anvil. Electrical connector 82 also providesthermal isolation or discontinuity between the two flex cables.

A diagram illustrating a side view of the example cryostat system usinga single printed flexible cable is shown in FIG. 3B. As described supra,the use of two flex cables with a thermal/electrical break between themversus using a single cable is more energy efficient. Use of a singleflex cable, however, may also be used. In this case, the flex cablestill passes through a thermal anchor consisting of matched thermallyconductive components 88, 89. The connector that normally couples thetwo cables (FIG. 3A) is now eliminated as there is a direct connectionbetween the air side of the vacuum chamber and the sample board on thevacuum side. Thus, the thermal isolation that was formerly provided bythe connector 82 (FIG. 3A) has been removed.

A diagram illustrating a cross sectional view of the example cryostatsystem including heat shield and cooling tower is shown in FIG. 4 . Thecryostat 60 comprises cold head 62, mounting plate 64, TV-flex circuit66, spiral cable 72, cryocooler first stage shaft 80, first stage plate78, cryo-flex PCB termination 84, cryo-flex cable 86, connector 82,cryocooler second stage shaft 96, second stage plate 90, second stagemounting plate 94, PCB assembly 92, PCB assembly mounting suspensionsprings 93, sample board 106, sample board mounting suspension springs104, pillars or spacers 102 that connect the sample board 106 to thesecond stage cold plate 90 and mounting plate 94, adjustable magnets 100that straddle the sample integrated circuit, and vacuum chamber bucket140.

It is noted that both the PCB assembly 92 at the end of the cryo-flexcable 86 and the sample board 106 are suspended to allow fordifferential thermal expansion and contraction between temperaturechanges from low working temperatures (i.e. 3K) to room temperature(i.e. 300K).

A diagram illustrating a side view of the example cryostat systemshowing the cryostat cable in more detail is shown in FIG. 5 . The firststage cooling shaft 80 is coupled to the first stage cold plate 78 whichis maintained at approximately 30K. The second stage cooling shaft 96extends downward to second stage cold plate 90 and mounting plate 94which is maintained at 3 degrees K. The TV-flex cable 72 terminates viaPCB assembly 76 at connector 82. The cryo-flex cable 86 extends downwardfrom PCB assembly 84 making a small loop and rises upward to saddle 88and anvil 89 which form a thermal anchor at the first stage temperatureof degrees K. The cryo-flex cable continues downward towards the secondstage cooling plate and is terminated in PCB assembly 92 connected tothe sample board (not shown). Mounting screws with springs provideadjustable tension between the cold contact plate and the integratedcircuit. Magnet assembly 100 straddles the sample board as described inmore detail infra.

A diagram illustrating the connector interface between the two flexcables in more detail is shown in FIG. 6 . The connector 82 providesgood electrical conductivity between the TV-flex PCB assembly 76 and thecryo-flex PCB assembly 84. The connector 82 is adapted, however, toprovide poor thermal conductivity and to thermally isolate the two flexcables. This helps prevent heat from traveling between the TV-flex cable72 and the cryo-flex cable 86. The TV-flex PCB assembly 76 is alsomechanically and thermally fastened to the first stage cold plate 78which maintains the temperature at 30K. The saddle 88 and matchingcomplimentary anvil 89 mechanically and thermally clamp the cryo-flexcable to form a thermal anchor to the first stage cold plate 78.

A diagram illustrating the suspended sample board mechanism in moredetail is shown in FIG. 7 . As described supra, the second stage coolingshaft 96 terminates on cold plate 90 and mounting plate 94. The sampleboard 106 is electrically coupled through PCB connector 134 to PCBassembly 92 at the end of the cryo-flex cable 86. Metal (e.g., copper)pillar spacers 122 mechanically and thermally connect metal contactplate 124 to the second stage cold plate and mounting plate 94 whilecreating space for magnet assembly 100 that sandwiches the integratedcircuit 126 being cooled. Set screws and springs 110 mechanicallyisolate the PCB assembly 92 from the contact plate 124 and second stagecold plates. Additional set screws and springs 104 mechanically isolatethe sample board assembly 106 from the contact plate 124. In addition,they enable the adjustment of the force between the sample board andintegrated circuit against the contact plate 124 which is physically andthermally in contact with the integrated circuit.

The magnet assembly 100 is adapted to be adjustably positioned above andbelow the quantum integrated circuit (IC) and functions to apply amagnetic field to control the spin of one or more quantum particles inthe quantum IC.

Alternatively, the magnets may be omitted and the pillar spacers in thiscase would not be needed and the contact plate would be fasteneddirectly to the cold plate 90. In another embodiment, the magnets aremounted so as not to apply a vertical magnetic field as shown in FIG. 7, but rather to apply a horizontal magnetic field to control the spin ofone or more quantum particles in the quantum IC on the sample PCB. Inthis embodiment, the one or more magnets above and below the quantum ICwould be arranged horizontally or on a steep angle.

Wheel assembly 128 enables adjustment of the height of the magnetassembly 100 above and below the integrated circuit. Plate 130 andpillars 132 provide mechanical support for the magnet assembly. Inaddition, RF connectors 120 receive RF signal inputs to the integratedcircuit on the sample board.

In an alternative embodiment, the TV flex circuit is mounted on the sideof the vacuum chamber rather than the top. The TV flex circuit uses thesame vacuum sealing utilizing 0-rings to seal against the annularsealing region portion of the flex circuit. A spiral tab extends intothe vacuum chamber and is terminated in a thermally isolating electricalconnector.

A diagram illustrating an outside view of an example trans-vacuumflexible printed circuit installed in a vacuum chamber with a rigidprinted circuit board tab extending outward is shown in FIG. 8 . Theflex tab 16 and rigid PCB 18 of the TV flex circuit is shown extendingoutward from the vacuum chamber through a tension relief assembly 44, 46that bends and holds the cable in place and ensures the flex circuit isnot overstressed. Note that it does not play a role in thermal isolationor vacuum sealing. The cover plate 30 is shown bolted in position to theperimeter of the hole in the vacuum chamber 34 via a plurality of bolts32.

In the configuration shown, the annular sealing region 12 (FIG. 2A) is agenerally annular shaped continuous laminated flexible material whoseouter perimeter is offset from the outer (e.g., octagonal) shape of acover plate 30 (FIG. 8 ). In this example configuration, the sealexpresses eight holes around the outer perimeter positioned to clearconnector bolts 32 that hold the cover plate 30 to the perimeter of ahole in the vacuum chamber 34. The signal and power traces run acrossthis flat annular seal, with an axial, flexible tab 16 out of thesealing region that develops into a flat and rigid multi-contactconnector PCB 18 on the air side of the vacuum chamber. Those samesignal and power traces run across this annular seal in the otherdirection, towards the center of it, developing into a flat and rigidmulti-contact connector PCB 76 vacuum side of the vacuum chamber.

A diagram illustrating a forward cutaway view of an example trans-vacuumflexible printed circuit installed in a vacuum chamber with an O-ringseated against an annular sealing region is shown in FIG. 9 . In thisview, an O-ring seal 36 is shown seated in a front groove 38 cut intothe back side of the cover plate 30. The O-ring 36 is adapted to sealaround the annular sealing region 12. Holes 22 allow bolts to passthrough to fasten the cover plate 30 to the vacuum chamber 34.

A diagram illustrating a rear cutaway view of an example trans-vacuumflexible printed circuit installed in a vacuum chamber with an O-ringseated against an annular sealing region is shown in FIG. 10 . In thisview, an O-ring seal 40 is shown seated in a back groove 42 cut into thefront perimeter of the hole in the vacuum chamber 34. The O-ring 40 isadapted to seal around the annular sealing region 12. Holes 22 allowbolts to pass through to fasten the cover plate 30 to the vacuum chamber34.

A diagram illustrating a side sectional view of a first exampletrans-vacuum flexible printed circuit installed in a vacuum chamber withan annular sealing region sandwiched between two O-rings is shown inFIG. 11A. The TV flex circuit 10 is shown mounted and sealed over thehole in the vacuum chamber 34. The annular sealing region 12 issandwiched between the outer surface of the perimeter of the hole in thevacuum chamber and the inner surface of the cover plate 30. Grooves 42,38 hold elastomeric O-rings 40, 36, respectively, that sandwich theannular sealing region 12 to create the vacuum seal. Electrical signalspass from PCB connector 18 through flex tab 16 through saddle 44, 46,cross the annular sealing region axially or otherwise and pass throughspiral flex tab 14 to PCB 20.

Since the cover plate 30 is exposed to air it typically sits at roomtemperature 300K. This is the temperature that the TV flex cable getsanchored. The temperature inside the vacuum chamber is maintained at30K. Thus, there is a gradient along the TV-flex cable tab to the firststage rigid PCB connector. Note that heat convection is minimal becauseof the vacuum maintained inside the chamber. Radiated heat is handled bythe first stage cooler which in one embodiment is rated at 50 W.Radiated heat is received and reflected via the heat shield made of goldplated copper.

The flexible printed circuits of the present invention are typicallyconstructed from well-known materials used such as Kapton, polyimide,etc. Any material used should preferably have low outgassing, besuitable for use in a vacuum and at low temperatures, have goodelectrical performance, exhibit low insertion loss and good isolation.

In one embodiment, the annular flex material sealing region issufficiently wide for annular vacuum seals (e.g., elastomeric O-rings36, 40, etc.) to seal off on both its top side and bottom side, creatingvacuum seals between the outer sealing surface of the hole into thevacuum chamber and the underside of the flex material sealing region 12,and the top side of the flex material sealing region and the undersidesealing surface of the vacuum cover plate 30.

Note that in one embodiment, the annular vacuum seals can be concentric,and they can be the same size so they compress the TV flex materialsealing region directly between them. Alternatively, the centers of theannular vacuum seals can be offset and/or their diameters can bedifferent to each other, so that they compress the flex material sealingregion between themselves and a rigid component surface opposite them,i.e. (1) the outer sealing surface of the hole into the vacuum chamber,(2) the underside sealing surface of the vacuum cover plate, or (3)other intermediate sealing components or features. In addition, the twoO-ring seals do not necessarily have the same diameter as one may have alarger diameter than the other to improve sealing. This alternativeembodiment is shown in FIG. 11B where the inner O-ring 40 on the vacuumside has a smaller diameter than the outer O-ring 36 on the air side.Note that in the embodiment shown, a ‘buffer’ distance or gap 37 isinserted between the two O-ring channels to improve the vacuum sealingperformance. In addition, the inner O-ring 40 on the vacuum side mayhave a larger diameter than the outer O-ring 36 on the air side.

Moreover, the annular vacuum seals (e.g., O-rings) can employ differentshaped cross-sections, such as round, oval, square, rectangular,X-shaped or any combination of these cross-section shapes. Further, theannular vacuum seals are not limited to elastomeric seals and maycomprise non-elastomeric seals such as crush seals. In addition, the TVflex circuit and/or the annular vacuum seals can be non-circular in planview.

The flexible tabs into and out of the TV flex circuit annular sealingregion can be otherwise advantageously shaped. It can be shaped as aspiral on the inside, for example, to extend the service length of theinner flex tab or otherwise control its path into the vacuum chamber.Similarly for the outward pointing tab, but with greater design freedombecause of the unlimited space around the outside of the annular vacuumseal.

Note that the flexible tabs into and out of the trans-vacuum sealingregion need not traverse the vacuum seal shape axially, but canadvantageously traverse the seal at other angles from axial totangential, and/or along indirect paths around the annular vacuumsealing region.

Note also that the electrical traces that traverse the trans-vacuumsealing region can be split to form multiple connectors and connectortypes into and out of the vacuum chamber. Thus, any number of connectorsmay extend out of the annular sealing region into the air side as wellas extend out of the annular sealing region into the vacuum chamberside.

Note that in one embodiment, the connector connecting the TV-flex andcryo-flex cables are not fabricated from copper but rather from copperberyllium or copper phosphor bronze. Both of these metals are poorelectrical conductors at 30K thus the connector contacts are goldplated. Preferably, the connector is also a good thermal isolator makinga high thermal ‘impedance’ connection to prevent any heat present on theflex cable from traveling toward the sample board. Typically, there is athermal gradient along the TV-flex cable. Thus, a thermal break point isplaced along the path of the TX-flex cable, cryo-flex cable, or bothcables. It is noted that the copper that is used for the traces of thecables gets more conductive as it gets colder. Therefore, the largestgradient occurs near the 300K side (i.e. the air side) of the cable.Both the connector and the thermal anchor provide a needed thermalbreak, hence the use of two cables rather than one where the thermalisolation helps to keep the heat away from the sample board.

In one embodiment, one or more RF signals pass from outside the vacuumchamber, through the wall of the chamber via connectors mounted in holesto the one or more RF connectors 120 (FIG. 7 ) mounted on the suspendedsample board 106. These signal may comprise clock and in/out datasignals forming a high speed interface (HSIO).

In an alternative embodiment, the RF signals are generated within thevacuum chamber via circuitry on the rigid PCB terminal end of the TVflex cable. A diagram illustrating example RF signal cables extendingfrom the trans-vacuum flexible printed circuit to the suspended sampleboard is shown in FIG. 12 . In this embodiment, rather than pierce thewalls of the vacuum chamber, a lower frequency reference signal (e.g.,<50 MHz) is provided over the TV flex cable from the air side and aphase locked loop (PLL) or other suitable frequency multiplier circuitis used to generate the required clock signal (e.g., in the gigahertzfrequency range) and any other required clocks and data signals. The PLLcircuitry and one or more RF connectors are mounted on the PCB assembly76 and RF cables 121 provide a connection between the PCB assembly 76and the RF connectors 120 on the sample board 106. This eliminates theneed to provide holes in the vacuum chamber simplifying fabrication andreducing potential vacuum leakages.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediary components. Likewise, any two componentsso associated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The use of introductory phrases suchas “at least one” and “one or more” in the claims should not beconstrued to imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first,” “second,” etc. are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. As numerousmodifications and changes will readily occur to those skilled in theart, it is intended that the invention not be limited to the limitednumber of embodiments described herein. Accordingly, it will beappreciated that all suitable variations, modifications and equivalentsmay be resorted to, falling within the spirit and scope of the presentinvention. The embodiments were chosen and described in order to bestexplain the principles of the invention and the practical application,and to enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A flexible wiring apparatus for use in acryostat, comprising: a first flexible printed circuit adapted to besealed in a vacuum chamber of the cryostat and having a plurality ofelectrically conductive traces for passing electrical signals between anair side and a vacuum side of the cryostat; a second flexible printedcircuit coupled to a sample board held at a first cryogenic temperature;an electrical connector operative to electrically couple said firstflexible circuit to said second flexible circuit while providing thermalisolation between said first flexible circuit and said second flexiblecircuit; and a thermal anchor operative to clamp said second flexiblecircuit to a second cryogenic temperature thereby providing a thermalbreakpoint between said first cryogenic temperature within said vacuumchamber and ambient temperature outside said vacuum chamber.
 2. Theflexible wiring apparatus according to claim 1, wherein said firstflexible printed circuit and said second flexible printed circuitmaterial comprise Kapton and/or polyimide.
 3. The flexible wiringapparatus according to claim 1, wherein said electrical connectorcomprises gold plated copper beryllium or copper phosphor bronzecontacts.
 4. The flexible wiring apparatus according to claim 1, furthercomprising a PCB assembly operative to terminate said first flexibleprinted circuit and which is mechanically and thermally fastened to afirst stage cold plate maintained at said second cryogenic temperature.5. The flexible wiring apparatus according to claim 1, furthercomprising a PCB assembly operative to terminate said first flexibleprinted circuit incorporating one or more RF connectors and circuitryfor generating one or more high frequency RF signals from a lowfrequency reference signal.
 6. The flexible wiring apparatus accordingto claim 1, wherein said thermal anchor comprises matched thermallyconductive components adapted to sandwich said second flexible circuitand which is mechanically and thermally fastened to a first stage coldplate maintained at said second cryogenic temperature.
 7. The flexiblewiring apparatus according to claim 6, wherein said matched thermallyconductive components comprise copper.
 8. The flexible wiring apparatusaccording to claim 1, wherein said first flexible printed circuit islocated at a top or side of said vacuum chamber.
 9. The flexible wiringapparatus according to claim 1, further comprising a PCB assemblyoperative to electrically terminate said second flexible printed circuitto said sample board, said PCB assembly compliantly suspended from saidsample board to enable contraction and expansion thereof when cooling toor warming from said first cryogenic temperature.
 10. The flexiblewiring apparatus according to claim 1, wherein said first and secondflexible printed circuit further comprise a plurality of printed layersincluding one or two outer electromagnetic shielding layers consistingof a non-solid mesh pattern selected from the group consisting ofdiamonds, hexagons, honeycombs, octagons, and polygons
 11. A flexiblewiring apparatus for use in a cryostat, comprising: a flexible printedcircuit, including a flat laminated flexible material having an annularshaped sealing region able to be vacuum sealed between a cover plate anda perimeter of a hole in a vacuum chamber of the cryostat; a pluralityof electrically conductive traces that cross said annular shaped regionthereby passing electrical signals between an air side and a vacuum sideof the cryostat; a first PCB assembly terminating said plurality ofelectrically conductive traces on the air side of the cryostat forconnection to an external host computer; a second PCB assemblyterminating said plurality of electrically conductive traces on thevacuum side of the cryostat for connection to a sample circuit boardcontaining an integrated circuit cooled to a first cryogenictemperature; and a thermal anchor operative to clamp said flexibleprinted circuit to a second cryogenic temperature thereby providing athermal breakpoint between said first cryogenic temperature within saidvacuum chamber and atmospheric temperature outside said vacuum chamber.12. The flexible wiring apparatus according to claim 11, wherein saidflexible printed circuit comprises Kapton and/or polyimide.
 13. Theflexible wiring apparatus according to claim 11, wherein said thermalanchor comprises matched thermally conductive components adapted tosandwich said flexible printed circuit and which is mechanically andthermally fastened to a first stage cold plate maintained at said secondcryogenic temperature.
 14. The flexible wiring apparatus according toclaim 13, wherein said matched thermally conductive components comprisecopper.
 15. The flexible wiring apparatus according to claim 11, whereinsaid first flexible printed circuit is located at a top or side of saidvacuum chamber.
 16. The flexible wiring apparatus according to claim 11,further comprising a PCB assembly operative to electrically terminatesaid flexible printed circuit to said sample board, said PCB assemblymechanically suspended from said sample board to enable contraction andexpansion thereof when cooling to or warming from said first cryogenictemperature.
 17. The flexible wiring apparatus according to claim 11,wherein said flexible printed circuit further comprises a plurality ofprinted layers including one or two outer electromagnetic shieldinglayers consisting of a non-solid mesh pattern selected from the groupconsisting of diamonds, hexagons, honeycombs, octagons, and polygons 18.A flexible wiring apparatus for use in a cryostat, comprising: a firstflexible printed circuit, including: a flat laminated flexible materialhaving an annular shaped sealing region able to be vacuum sealed betweena cover plate and a perimeter of a hole in a vacuum chamber of thecryostat; a plurality of electrically conductive traces that cross saidannular shaped region thereby passing electrical signals between an airside and a vacuum side of the cryostat; a second flexible printedcircuit coupled to a sample board held at a first cryogenic temperature;an electrical connector operative to electrically couple said firstflexible circuit to said second flexible circuit while providing thermalisolation between said first flexible circuit and said second flexiblecircuit; and a thermal anchor operative to clamp said second flexiblecircuit to a second cryogenic temperature thereby providing a thermalbreakpoint between said first cryogenic temperature within said vacuumchamber and ambient temperature outside said vacuum chamber.
 19. Theflexible wiring apparatus according to claim 18, further comprising aPCB assembly operative to terminate said first flexible printed circuitand which is mechanically and thermally fastened to a first stage coldplate maintained at said second cryogenic temperature.
 20. The flexiblewiring apparatus according to claim 18, wherein said thermal anchorcomprises matched thermally conductive components adapted to sandwichsaid second flexible circuit and which is mechanically and thermallyfastened to a first stage cold plate maintained at said second cryogenictemperature.